This invention relates to synchronous motors and, more particularly, to a self-starting, high running torque, synchronous motor. Small synchronous motors are widely used in timing devices such as clocks and appliance timers. Those motors have a rotor which is provided with a number of permanently magnetic poles about its periphery. The rotor is mounted within a stator which includes a number of windings in the form of an annulus. Poles are provided on the stator which change polarity as a function of the frequency. As is known, synchronous motors may turn in either direction, depending on the relative at-rest position of the rotor and stator. Therefore, various devices have been proposed to ensure rotation of the rotor in a predetermined direction, and one such device is disclosed in U.S. Pat. No. 3,307,086.
However, upon starting, the rotor may be in a balanced condition where the forces tending to move the rotor in both directions are balanced. Therefore, prior art synchronous motors have been provided with asymmetrical rotor or stator conditions so that the rotor will be urged to turn. Prior art synchronous motors have been provided with a relatively large number of rotor and stator poles, and it is customary to misalign a number of stator poles to produce an asymmetrical condition for starting. It was believed that for starting purposes a relatively large number of poles should be misaligned or offset from the remaining evenly spaced poles to increase the chances of the rotor poles to be in a starting condition without unnecessary hunting by the rotor. For example, one such prior art motor had a 22-pole rotor, with those poles being equally spaced, and a stator having a total of 20 poles, with 10 evenly spaced and 10 offset. The evenly spaced poles in such a motor are considered to be the running poles, since they provide an ideal field condition for running torque. The offset poles are called "starting poles" since they provide the asymmetric field conditions for starting purposes, but there exists a torque loss under running conditions. Prior art synchronous motors, therefore, were a compromise between optimum running conditions and optimum starting conditions.